Most constant velocity universal joints are sealed in order to retain grease inside the joint while keeping contaminants and foreign matter, such as dirt, water, and the like out of the joint. In order to achieve this protection, the constant velocity joint is usually enclosed at the open end of the outer race by a sealing boot made of rubber, thermoplastic or urethane. The opposite end of the outer race is sometimes formed by an enclosed dome known in the art as a “grease cap”. Such sealing and protection of the constant velocity joint is necessary because, once the inner chamber of the outer joint is partially-filled and thus lubricated, it is generally lubricated for life.
It is often necessary to vent the constant velocity joint in order to minimize air pressure fluctuations due to expansion and contraction of the air within the joint during operation of the joint. This is especially true, for example, in the case of tripod-type, plunging VL and mono block constant velocity joints.
As those skilled in the art will recognize, a tripod joint is characterized by a bell-shaped outer race (housing) disposed around an inner spider joint which travels in channels formed in the outer race. The spider-shaped cross section of the inner joint is descriptive of the three equispaced arms extending therefrom which travel in the tracks of the outer joint. Part spherical rollers are featured on each arm.
Plunging tripod joints are currently the most widely used inboard (transmission side) joint in front wheel drive vehicles, and particularly in the propeller shafts found in rear wheel drive, all-wheel drive and 4-wheel drive vehicles. A common feature of tripod universal joints is their plunging or end motion character. Plunging tripod universal joints allow the interconnection shafts to change length during operation without the use of splines which provoke significant reaction forces thereby resulting in a source of vibration and noise.
The plunging tripod joint accommodates end wise movement within the joint itself with a minimum of frictional resistance, since the part-spherical rollers are themselves supported on the arms by needle roller bearings. In a standard ball roller type constant velocity joint the intermediate member of the joint (like the ball cage in a Rzeppa constant velocity joint) is constrained to always lie in a plane which bisects the angle between the driving and driven shafts. Since the tripod type joint does not have such an intermediate member, the medium plane always lies perpendicular to the axis of the drive shaft.
A Plunging VL or “cross groove” type constant velocity joint consists of an outer and inner race drivably connected through balls located in circumferentially spaced straight or helical grooves alternately inclined relative to a rotational axis. The balls are positioned in a constant velocity plane by an intersecting groove relationship and maintained in this plane by a cage located between the two races. The joint permits axial movement since the cage is not positionably engaged to either race.
High speed fixed joints are used where transmission of high speed is required. High speed fixed joints allow articulation to an angle (no plunge) but can accommodate much higher angles than with a Cardan joint or other non-CV joints such as, for example, rubber couplings. There are generally three types of high speed fixed joints: (1) disk style that bolts to flanges; (2) monoblock style that is affixed to the tube as a center joint in multi-piece propshafts; and (3) plug-on monoblock that interfaces directly to the axle or T-case replacing the flange and bolts.
A high speed fixed joint generally comprises: (1) an outer joint member of generally hollow configuration, having a rotational axis and in its interior, a plurality of arcuate tracks circumferentially spaced about the axis extending in meridian planes relative to the axis, and forming lands between the tracks and integral with the outer joint part wherein the lands have radially inwardly directed surfaces; (2) an inner joint member disposed within the outer joint member and having a rotational axis, the inner joint member having on its exterior a plurality of tracks whose centerline lie in meridian planes with respect to the rotational axis of the inner joint member in which face the tracks of the outer joint member and opposed pairs, wherein lands are defined between the tracks on the inner joint member and have radially outwardly directed surfaces; (3) a plurality of balls disposed one in each pair of facing tracks in the outer and inner joint members for torque transmission between the members; and (4) a cage of annular configuration disposed between the joint members and having openings in which respective balls are received and contained so that their centers lie in a common plane, wherein the cage has external and internal surfaces each of which cooperate with the land surfaces of the outer joint member and inner joint member, respectively to locate the cage and the inner joint member axially.
Typically, constant velocity joints are vented by placing a small hole generally in the center of the grease cap or, in the case of mono block high speed fixed joints, by placing a hole in the vent plate. This allows for the passage of air in and out of the joint as needed, in order to prevent pressure buildup which occurs during operation of the joint. However, when the constant velocity joint is in a static state and not rotating, grease may settle in the vent hole, blocking it and hindering its function. This condition may create a pressure buildup and possibly result in joint failure due to a ruptured boot, among other things. During this static state, grease may also flow from the vent hole and out of the joint, thereby resulting in the loss of grease from the joint. This loss of lubricant could possibly lead to more frequent relubrication and maintenance, and eventually possible replacement of the joint. Still further, in off road, submerged, or other severe weather vehicle conditions, water and other contaminants may enter the joint through the vent hole and impair joint operation.
U.S. Pat. No. 4,319,467 issued to Hegler et al. discloses a sealed vent subassembly press fitted into the collar bore of a universal joint. The subassembly includes a vent disc which is nested in a seal disc to form a venting arrangement to the exterior of the housing by way of various holes and chambers. However, this vent hole may still be subject to grease buildup during a static state or operative state.
U.S. Pat. No. 6,010,409 issued to Johnson and assigned to GKN Automotive, Inc., the assignee of the present invention, discloses a vent regulator device for use in a constant velocity joint including a housing having an inner surface defining an inner cavity. The inner surface includes an annular portion, a domed portion which has a relatively small vent hole centrally located therein. The vent regulator device further includes a member having a first end and a second end where the first end is mounted to the inner surface of the housing and the second end is disposed proximate the vent hole. When the constant velocity joint is in one of either a static state or an active state rotating at speeds below a predetermined threshold, the vent hole is overlappingly covered by the first end of the member, thereby preventing grease from penetrating the hole. Moreover, when the constant velocity joint is in an active state rotating at speeds above the predetermined threshold, centrifugal forces cause the second end of the member to move away radially from the vent hole to allow venting of air therethrough.
U.S. Pat. No. 6,220,967 issued to Miller and assigned to GKN Automotive, Inc., the assignee of the present invention, discloses a constant velocity joint plug for use with a universal joint having a vent aperture. The joint plug comprises a substantially rigid elongate body having a first end and a second end with a vent cavity extending therebetween. A retention cap having an escape aperture is disposed adjacent the first end. The vent plug is fitted in the vent aperture and extends into the joint cavity above the grease fill line. In operation, pressure created in the joint cavity by grease volatility and high internal running temperatures (“overpressure”) is relieved through the vent cavity of the vent plug and released out of the joint by the escape aperture. Stabilization is continuous as the escape aperture releases air in direct relation to any increase in internal pressure of the joint.